Is a 99 sq ft backyard room a modular home?

It is built the way one is — manufactured and finished before it reaches you, then set down on site. What the term also covers is a dwelling unit, which is permitted, inspected and connected like a house. The Wavyroom Basic and Wavyroom Loft are backyard rooms of 99 sq ft, kept under the floor area jurisdictions exempt from a building permit.

How is this different from a prefab ADU?

An ADU is a dwelling unit: somebody lives in it, so it is permitted and inspected as living space, and water, sewer and a foundation are part of the project. A backyard room is accessory, non-habitable space in the yard. Whether anyone will be living in the room is the question that decides which of the two you are shopping for, and it is the first thing we ask.

Which cost items come with the permitted build and not with a backyard room?

Water and sewer, a foundation designed for the unit, service connections, plan review and inspections — each one a separate piece of work on the property. On the exempt side the room itself is the purchase, and what remains depends on the property: how the unit reaches the yard, where it sits, and how services get to it. We go through those with you against your address.

Do both models fit under the same exempt floor area?

Both are 99 sq ft, about 9.2 ㎡, under each of the area limits listed for California, IRC-based cities and Houston. Area is the first condition rather than the only one. California's exemption is written for a one-story structure, and the Loft carries a 43 sq ft loft under a 12 ft ceiling, so whether that reads as a second storey, and whether those 43 sq ft count toward floor area, are put to your local authority. Houston sets conditions beyond area as well.

Small modular home cost, 2 backyard models compared

Jurisdiction	Permit-exempt up to	Conditions
California	120 sq ft	CRC §R105.2 — one-story detached accessory structure. No height limit.
IRC-based states and cities (Oregon; Dallas and Austin, Texas, among others)	200 sq ft	IRC §R105.2(1). Austin adds a 15 ft height limit.
Houston, Texas	120 sq ft	Conditions beyond floor area apply here. We confirm them with your local office.

Wavyroom Basic	$23,500
Wavyroom Loft	$28,300

Two different projects get called a modular home. Both are built in a factory; they are not the same build.

One is a dwelling unit — a house, or an accessory dwelling unit (ADU) added to a lot someone already owns. The permit exemptions in section 3 are written for accessory, storage or non-habitable structures, so a unit built to be lived in is not what they cover. It goes through a building permit, with plan review and with inspections as the work proceeds.

The other is a backyard room: a detached, non-habitable space in your yard, kept inside the limits your jurisdiction sets for structures that need no building permit. Floor area is the first of those limits.

The Wavyroom Basic and the Wavyroom Loft are the second kind. Both are 99 sq ft, used as a home office, a studio, a workshop or a yoga room. Wavyroom is the backyard-room brand of Spacewavy, and we sell these two in the United States.

The conditions in section 3 show what sits on the other side of the line. Those exemptions are written for structures with no plumbing and no drainage, used for storage or kept non-habitable.

A unit built to be lived in has the opposite of that list. Water and sewer, a foundation designed for the unit, service connections, plan review and inspections are each a separate piece of work on the property, scheduled one by one.

On the exempt side, the room itself is the purchase. The unit is manufactured before it reaches you and set down on site in a day. What remains depends on the property — how the unit reaches the yard, where it sits, and how services get to it.

Give us your address and a description of the spot — access from the street, what is around it, what is already on the property. We go through the property-side items one by one with you before you order, and that is when the complete picture comes together.

A backyard studio is a detached, non-habitable space in the yard, and it can be installed without a building permit where it meets the limits and conditions the jurisdiction sets. Those rules are not the same everywhere. These are the ones we work from in the US:

Both of our rooms are 99 sq ft (about 9.2 ㎡), under each of the area limits above. The unit was sized to the 10 ㎡ (108 sq ft) line, the tightest area threshold among the markets we sell in, rather than to any single jurisdiction here.

Area is where each of these starts, not where the checking ends — the right-hand column is why.

California writes "one story" into its exemption. The Loft stands 12 ft tall and carries a 43 sq ft loft over part of the room. Whether a platform inside a single room reads as a second storey under that wording is for your local authority to say, and so is whether the loft's 43 sq ft counts toward floor area — that is answered municipality by municipality. We put both questions with you rather than answer them in advance.

Houston sets conditions beyond floor area, so the number alone does not settle it there. We confirm the rest with your local office before anything is ordered, and the same applies to any city or county that is not in the table.

A permit exemption is not a zoning exemption. Setbacks, lot coverage and permitted use are set by zoning. Utility hookups can need a permit of their own. HOA rules, and wildfire, flood or heritage overlays, apply on top. This holds in every jurisdiction above, so we check those items with you as well.

Both models hold 99 sq ft of floor: a backyard room under the area limits, installed in a day.

Both prices are for the unit.

The $4,800 between them buys height and what height makes room for. The Loft stands 12 ft against the Basic's 9.5 ft and carries a 43 sq ft loft over part of the room. It opens with a sliding door rather than a folding one, windows are included, and a desk-and-cabinet unit can be added to it.

Start with the Wavyroom Basic when one level holds what the room is for — a desk and a chair, a mat, a workbench. Look at the Wavyroom Loft when something has to go up and out of the way of the floor. Each guide takes that model line by line: the full spec, what the price covers, and the permit conditions as they apply to it.

Tell us the address and we will check it. We come back with what your jurisdiction allows there, which room fits, the price, and what delivery needs on site — Ask Wavyroom

Small modular home cost, 2 backyard models compared

Key takeaways

4. Where our two rooms sit

1. What a modular home can mean

2. Why that line changes what you pay for

3. Permit-exempt floor area, jurisdiction by jurisdiction

Frequently asked questions